The present invention relates to a device for reducing the line noise inside a rotary-wing aircraft, especially a helicopter.
More specifically, it applies to the reducing of noise in the flight deck and/or the passenger cabin of said aircraft.
It is known that, in a rotary-wing aircraft of this type, the acoustic spectra defined in the range between 20 Hz and 20 kHz are the result of the superposition of noises of differing origins, which can be categorized into two different groups depending on their spectral characteristics, namely pure sounds, or line noises, and broadband noises.
As is known, pure sounds or line noise, in particular, arise, as appropriate:
at the characteristic frequencies of the aircraft drivetrain; PA0 at the rotational frequencies of the rotor blades (main and tail rotor) and at the harmonics of these frequencies; PA0 at the rotational frequencies of the turbine engine compressor blades; and/or PA0 at the rotational frequencies of the fanblades of the fans that cool the main gearbox and/or electrical equipment, and at the harmonics of these frequencies, PA0 the noise of the boundary layer developing on the fuselage; PA0 the noise generated by the rotors; PA0 the airflow noise from the air intakes and jet pipes; PA0 the engine noise; and/or PA0 the noise of the circuits for air-conditioning or heating of the flight deck or the passenger cabin. PA0 reducing the vibration of the structure and/or of mechanical components, by damping or modifying the stiffness or the mass; PA0 attenuating the acoustic transmission, by deadening or modifying the stiffness or the mass; PA0 a double-skin effect, by shrouding the target source; PA0 acoustic absorption using fibrous or cellular material; and PA0 acoustic absorption using Helmholtz resonators. PA0 a noise reduction that is limited especially at low frequencies; PA0 a high increase in mass, which may be by several hundred kilograms in the case of a large-sized helicopter; PA0 a not insignificant loss of space, especially when using thick panels with a view to increasing the acoustic absorption effect; and PA0 acoustic leaks, particularly at the wiring lead-throughs and joints between the panels. PA0 at least one sensor for measuring the values of at least one vibrational and/or acoustic parameter representing a vibrational and/or acoustic effect of at least one source of noise of said aircraft; PA0 at least one mechanical means that can be controlled and is capable of creating a force capable of reducing the vibrational and/or acoustic effect of said source of noise; and PA0 a control unit for controlling said mechanical means on the basis of the values measured by said sensor. PA0 at least one engine fixing mount; PA0 one or more bearing(s) in the aircraft drivetrain; PA0 one or more bar(s) for fixing the main gearbox; PA0 a mechanical suspension of said main gearbox; PA0 the aircraft fuselage; PA0 a device for fixing lining panels to the structure; or PA0 a panel for lining the flight deck. PA0 one or more mount(s) for fixing said engine to the fuselage of the aircraft; PA0 one or more bearing(s) in said drivetrain; PA0 one or more bar(s) for fixing said main gearbox to the fuselage; PA0 a mechanical suspension of said main gearbox; PA0 the aircraft fuselage; or PA0 a device for fixing lining panels. PA0 values measured by one or more accelerometer(s) arranged on: PA0 values measured by one or more microphone(s) arranged in a cargo hold or in the compartment in which the main mechanical-power gearbox is located. PA0 it calculates, for each of the P sensors Cp, a value P1p that satisfies the equation: EQU P1p=P2p+.SIGMA.q(Tq,p.P3q), PA0 it calculates the sum: EQU .SIGMA.p.vertline.P1p.vertline..sup.2, PA0 it minimizes the above sum in order to deduce therefrom the commands for controlling said Q mechanical means Aq, which commands are sent to these means. PA0 in a first alternative form, said sensors Cp are microphones and the values P1p represent acoustic pressures; PA0 in a second alternative form, the sensors Cp are accelerometers and the values P1p represent accelerations; PA0 in a third alternative form, the sensors Cp are sensors capable of measuring a strain, a force, a displacement, a speed or an acceleration; and PA0 in a fourth alternative form, at least two of the previous three alternative forms are combined.
whereas broadband noises include, in particular, and as appropriate:
All these noises are of course annoying to pilots and passengers.
Thus, there are various known solutions for reducing such noises inside a rotary-wing aircraft, especially a helicopter.